Oligomerization and catalysts therefor

ABSTRACT

Sulphur-containing olefinic feedstocks are oligomerized over zeolite catalysts.

This invention relates to a process for the manufacture of highermolecular weight organic molecules from lower molecular weightmaterials, especially olefins, by oligomerization, to crystallinemolecular sieves suitable for use in the process, and the use of suchmolecular sieves in such reactions. The invention also relates to theoligomers produced and their use as feedstocks for further reactions.

Molecular sieve catalysts of many types have been used, or proposed foruse, in numerous chemical processes. Commercially, they have been used,for example, in hydrocarbon dewaxing, hydrocracking, toluenedisproportionation, and alkylation of aromatics. Among processes forwhich they have been proposed in the literature is the conversion byoligomerization of lower olefins, e.g., alkenes, to higher olefins,e.g., higher alkenes, for example the oligomerization of C₂ to C₆,especially C₃ and C₄, olefins to olefins in the C₆ to C₁₂ range, andoccasionally higher.

An example of a proposal to use crystalline molecular sieves ascatalysts for oligomerization is that described in EP-B-625 132, where ahydrated olefinic feedstock is oligomerized over a zeolite catalyst, thewater content of the feedstock being from 0.05 to 0.25 molar percent.The process is said to result in an increase in yield of highermolecular weight alkenes and to have the additional advantage ofenabling the reaction to be carried out at relatively low temperatures.Another example of such a proposal is that described in EP-B-746 538,where zeolites of the structure types MFI, TON, and MFS, in their acidforms, are used in oligomerization of propene and butene, the particularmembers of those structure type families used being ZSM-5, ZSM-22, andZSM-57. The patent is concerned with controlling the extent ofoligomerization, to obtain the desired proportions of or selectivity todimer, trimer, and higher oligomers, for use in downstream manufacturingprocesses. In the patent, methods of improving trimer yield aredescribed, the observation being made that higher conversion ratesproduce an oligomer mixture with a lower degree of branching.

The use of crystalline molecular sieves as catalysts has been found,however, to be subject to certain limitations in practice. Thefeedstocks used are frequently refinery products and may contain sulphurcompounds. In commercial processes customarily using such feedstocks as,for example, alkylation of aromatics and toluene disproportion sulphurhas to be removed before the feedstock contacts the catalyst.Exceptionally, if the feed contains hydrogen as, for example, indewaxing and hydrocracking, sulphur removal may not be necessary as thehydrogen present appears to stabilize the catalyst.

Our experiments have shown that under conditions normally used forolefin oligomerization over molecular sieve catalysts,sulphur-containing feedstocks may reduce catalyst activity and lifetime.However, it has now surprisingly been found that the presence of sulphurdoes not appear to have adverse effects on the reaction process itself.Indeed, provided oligomerization is carried out at a temperature higherthan that which would otherwise have been chosen for the reactionconcerned, the effect on catalyst activity and life may be mitigated,minimal, or even of advantage.

The temperature appropriate to mitigate the adverse effects of sulphurcompounds will vary, depending on the catalyst being used, the olefinicspecies being oligomerized, the specific sulphur compound or compoundsand their proportions present in the feedstocks. An appropriate minimumtemperature may, however, be readily identified by routine experiment.

The present invention accordingly provides a process for theoligomerization of an olefinic feedstock which comprises contactingunder oligomerization conditions an olefinic feedstock comprisingsulphur-containing compounds at an elevated temperature with a catalystcomprising at least one crystalline molecular sieve selected from sieveshaving the TON and MFS structure types, and recovering a productcontaining at least one olefin oligomer.

In this specification, the term “structure type” is used in the sensedescribed in the Structure Type Atlas, Zeolites 17, 1996. Examples ofTON structure type zeolites include ZSM-22, ISI-1, Theta-1, Nu-10, andKZ-2, and of MFS include ZSM-57, all preferably in their H- or acidform.

The crystalline molecular sieve is advantageously ZSM-22 or ZSM-57.ZSM-22 and its manufacture are described in, for example, U.S. Pat. No.4,556,477 and WO 93/25475, and ZSM-57 and its manufacture in EP-A-174121 and U.S. Pat. No. 4,973,870, the disclosures of all of which areincorporated herein by reference. Mixtures of two or more molecularsieves may be used, e.g., a mixture of ZSM-22 and ZSM-57.

A molecular sieve crystallite size advantageously up to 5 μm, preferablywithin the range of from 0.05 to 5 μm, more especially from 0.05 to 2μm, and most preferably from 0.1 to 1 μm, may be employed. The molecularsieve may be supported or unsupported, for example in powder form, orused as an extrudate with an appropriate binder. An as-synthesizedmolecular sieve is advantageously converted to its acid form, forexample by acid treatment, e.g., by HCl, or by ammonium ion exchange,and subsequent calcination before use in the process of the invention.The calcined materials may be post-treated as by steaming. Although theinvention will be described with reference to zeolites proper, it ispossible to use, as is known in the art, a material in which silicon andaluminium have been replaced in whole or in part by other elements,silicon more especially by germanium or phosphorus and aluminium moreespecially by boron, gallium, chromium and iron, materials containingsuch replacement lattice elements also being termed zeolites, and theterm is used in the broader sense in this specification.

The olefin feedstock advantageously contains olefins having from 2 to 12carbon atoms, preferably from 2 to 6 carbon atoms, and is advantageouslyan alkene-containing feedstock. The feedstock itself may be or comprisean oligomer, especially a dimer, especially one provided by recycling apart of a product stream. The feed preferably contains propene, butenes,pentenes and/or hexenes; the invention is especially applicable topropene and butene oligomerization.

As indicated above, the feedstock contains sulphur-containing compounds.The feedstock advantageously contains within the range of from 1 to 100,more advantageously up to 50, still more advantageously up to 30,preferably up to 20, more preferably up to 5, and still more preferablyup to 2, ppm by volume of such compounds. It is within the scope of theinvention to reduce the proportion of sulphur compounds from above theupper end of any of the given ranges, for example about 200 ppm, towithin any of the ranges, and also to reduce the proportion from withina less preferred range to a more preferred range. A typicallyencountered feedstock may have from 1 to 30 or from 2 to 20 ppm byvolume of sulphur compounds, and the invention is well suited to suchfeedstocks.

The sulphur content is conveniently ascertained by gas chromatographicanalysis using peak areas normalized with reference to a COS standard.

As examples of sulphur-containing compounds, there may be mentioned,more especially, saturated aliphatic compounds, for example, thiols,sulphides, including cyclic sulphides, and disulphides. Typicalcompounds include, for example, hydrogen sulphide, dimethyl sulphide,diethyl sulphide, ethyl methyl sulphide, n-propyl sulphide, 1- and2-propanethiols, 1-butanethiol, 1,1-methylethylthiol, ethyl methyldisulphide, dimethyl disulphide and tetrahydrothiophene.

Reaction conditions for the process of the invention may be, with theexception of the temperature and the presence of the sulphur compound orcompounds, in accordance with conditions operative for prior artprocesses for oligomerization of the same olefin or olefins.

The olefinic feedstock may be fed to the reaction zone in the liquid or,preferably, the supercritical phase. The feedstock may contain water,either present from the feedstock raw material or by addition.

The feedstock advantageously comprises from 0.05 to 0.25, preferablyfrom 0.06 to 0.20 and more preferably from 0.10 to 0.20, molar % waterbased on the total hydrocarbon content of the feedstock. If desired orrequired, the natural water content of the feedstock may be increased,for example, by being passed through a thermostatted water saturator.Since the amount of water required to saturate the feedstock will dependupon the temperature and composition of the feedstock, control of thewater content may be effected by appropriate control of the temperatureof the feedstock.

The feedstock may also comprise an inert diluent, for example, asaturated hydrocarbon. That other hydrocarbon is included in thehydrocarbon content for the purposes of calculation of the watercontent.

Operating temperatures for olefin oligomerization have variously beenreported in the literature as being between 80° C. and 350° C. Towardand above the upper end of the range, de-oligomerization rates increaseand may predominate over the oligomerization reaction, providing theupper limit to practical operation.

As indicated above, once the person skilled in the art is in possessionof the invention, it is a matter of routine experiment to ascertain, fora given feedstock and catalyst, the minimum and optimum temperatures foroperation within the general ranges of 100° C. to 350° C., especially135° C. to 350° C. and more especially 150° C. to 300° C. In general, atemperature of at least 160° C. has been found advantageous. Thefollowing combinations are given as examples only.

In MFS (typically ZSM-57)-catalysed reactions, an operating temperatureof at least 160° C. and up to about 220° C. is advantageous, at least170° C. is preferred, and at least 200° C. is more preferred. An MFScatalyst is preferred when the feedstock is propene and the targetoligomers are nonenes.

In TON (typically ZSM-22) catalysed reactions, an operating temperatureof at least 190° C., preferably 200° C., is advantageous, at least 220°C. is preferred, and at least 250° C. is more preferred. An advantageousupper limit is 350° C.; a preferred upper limit is 300° C. A TONcatalyst is preferred when the feedstock is butene and the targetoligomers are low-branched octenes.

It will be appreciated that, to maintain desirable conversion rates, itmay be advantageous to increase reaction temperatures with the time thecatalyst is on stream.

The pressure is advantageously in the range of 5 to 10 MPa, preferablyfrom 6 to 8 MPa. The olefin hourly space velocity is advantageously inthe range of from 0.1 to 20, preferably from 1 to 10, and morepreferably from 1.5 to 7.5, hr⁻¹.

When the oligomer product is to be used as starting material for certainpurposes, e.g., in the manufacture of certain plasticizer or detergentgrade alcohols, it is desirable to minimize the degree of branching ofthe product.

The degree of branching of the olefin oligomer may be controlled to someextent by operating temperature, higher temperatures normally yielding alower degree of branching (branchiness). The olefin branchiness largelydetermines that of any downstream product, for example plasticizer ordetergent grade alcohols, produced, for example, by the oxo process,from the oligomer olefins. The users of such products, and in turn theirdownstream products, for example plasticizer esters, have strictspecifications for various properties which the suppliers have to meet,and these specifications typically require branchiness to be within adefined range, usually a low range.

However, when an oligomerization operation is started up using freshcatalyst, the catalyst is highly active and, since the oligomerizationis exothermic, there is a serious risk of reactor runaway. It istherefore normally necessary to operate initially at a low temperatureand only reach the desired operating temperature over a prolongedperiod, during which substantial quantities of product are produced.This portion of the product will be of greater branchiness than thatproduced later, thereby increasing the average branchiness of theproduct, increasing the difficulty of meeting the customer'sspecification.

It has surprisingly been found that using a sulphur-containing feed asdescribed herein in some way controls the initial over-activity of thecatalyst, enabling the reaction to be started up at, or close to, thedesired operating temperature.

The invention accordingly also provides a process for controlling theactivity in an oligomerization reaction of a catalyst comprising atleast one crystalline molecular sieve selected from sieves of the TONand MFS structure types, which comprises contacting the molecular sievewith a sulphur compound-containing olefinic feedstock.

The invention accordingly also provides a process for controlling thedegree of branching of the product of an oligomerization reaction whichcomprises contacting under oligomerization conditions a sulphurcompound-containing olefinic feedstock with a catalyst comprising atleast one crystalline molecular sieve selected from sieves having theTON and MFS structure types.

The invention accordingly also provides the use of an elevatedtemperature in such a reaction to control the degree of branching of theoligomeric product.

Advantageously, the sulphur content of the feedstock is from 1 to 100ppm by volume.

The effect on the degree of branching is especially evident when thefeedstock is propene; with ZSM-22, the branchiness of the trimer issignificantly reduced; with ZSM-57, branchiness of both dimer and trimeris reduced.

The present invention also provides a crystalline molecular sieve of theTON or MFS structure type having absorbed therein or adsorbed thereon atleast one sulphur-containing compound. Advantageously, the crystallinemolecular sieve is ZSM-22 or ZSM-57. Advantageously, the sulphurcompound is, or is derived from, one of the groups specified above, andpreferably is, or is derived from, one of the specific compoundsidentified above. Advantageously, the crystalline molecular sieve havinga sulphur-containing compound absorbed therein or adsorbed thereon isone obtainable by, and preferably one obtained by, use as anoligomerization catalyst for a sulphur compound-containing feedstock.

The oligomers produced by the process of the present invention are aunique mixture of isomers, the members of which fall into five types ofskeletal structures, which areCH═CH₂  Type ICH═CHR′  Type IIRRC═CH₂  Type IIIRR′C═CHR″  Type IVRR′C═CR″R′″  Type Vwhere R, R′, R″ and R′″ are alkyl groups. The olefin type may beidentified by proton NMR analysis. Especially in combination with thecontrolled average degree of branching, the oligomer products of theinvention have advantages over those produced by traditional, e.g.,supported phosphoric acid catalysed, processes. These are primarily alower average degree of branching, and a lower proportion of Type Volefins, making them more suitable for onward processing, e.g., higheralcohol, aldehyde, and acid manufacture, because of a desirablereactivity when the oligomeric composition is subjected to the oxoprocess (hydroformylation).

The present invention accordingly also provides an oligomeric hexenemixture having an average degree of branching of at most 0.95,especially one within the range of from 0.92 to 0.95, and a maximum TypeV content of 6%, preferably 5%.

The present invention further provides an oligomeric nonene mixturehaving an average degree of branching of at most 2.0, and advantageouslyin the range of 1.5, preferably 1.78, to 2.0, more advantageously 1.78to 1.86, and having a type V olefin content of at most 14%, preferablywithin the range of 10 to 14%, especially one obtainable by ZSM-22catalysed oligomerization, especially in the presence of sulphur.Advantageously, the Type IV olefin content is within the range of 58 to60%; advantageously the Type III olefin content is within the range of7.25 to 7.75%; advantageously the Type II olefin content is within therange of 18.5 to 20%, and advantageously the Type I olefin content is1.2 to 2.2%.

The invention further provides an oligomeric dodecene mixture having anaverage degree of branching of at most 2.75, advantageously in the rangeof 2.70 to 2.75, and advantageously one having a type V olefin contentof at most 19%, and preferably within the range of from 16 to 19%,especially one obtainable by ZSM-22 catalysed oligomerization,especially of propene, especially in the presence of sulphur.Advantageously, the type IV olefin content is within the range of 59 to62%; advantageously the Type III olefin content is within the range 4.8to 5.7%; and advantageously the Type II olefin content is within therange 14 to 15%.

As indicated above, the oligomers of the invention are especiallysuitable as feedstocks for further processing, including at least one ofthe following: fractionation; hydrogenation; hydroformylation;oxidation; carbonylation; etherification; epoxidation, and hydration.The hydrogenated oligomeric octenes may comprise, for example, 12 to 15%2-methylheptane; 22 to 28% 3-methylheptane; and 7 to 9% 4-methylheptane.These are especially readily obtainable by oligomerization using acatalyst comprising ZSM-22.

The eventual products may be alcohols, produced for example byhydroformylation and hydrogenation; esters, in which the alcohols areesterified as with inorganic or organic acids, including carboxylicacids, especially polycarboxylic acids; aldehydes, acids, in which thehydroformylation products are oxidized and hydrogenated, and numerousother end uses.

The esters with polycarboxylic acids are especially valuable asplasticizers, and the invention further provides plasticizercompositions comprising the esters, and polymeric compositions,especially of vinyl polymers, more especially PVC, comprising theesters, and shaped structures formed of the plasticized polymericcompositions.

EXAMPLES

The following examples, in which parts and percentages are by weightunless otherwise indicated, illustrate the invention.

All feeds used in the examples were hydrated by passage through a watersaturator at 25° to 40° C.

Olefin monomer conversion rates were derived from gas chromatographicanalysis using peak areas normalized to the total sum of the paraffinsin the feed as internal standard, conversion being expressed as:${{conversion}\quad\%} = {100\left\lbrack {1 - \frac{A\quad{{o.m.}/A}\quad{paraffins}}{A^{o}\quad{{o.m.}/A^{o}}\quad{paraffins}}} \right\rbrack}$

-   -   where A represents chromatographic peak area in product (wt %),        A ° represents chromatographic peak area in feed (wt %)    -   and o.m. represents olefin monomer(s).

Selectivity to a given oligomer (dimer, trimer, etc.) is also determinedfrom gas chromatographic peak areas, after hydrogenation of the productstream.

Example 1

In this example, butene oligomerization was carried out over acommercial ZSM-22 catalyst (ZSM-22 (75%) supported on alumina), at aweight hourly space velocity of 6.8 h⁻¹, on a 60 to 65% butenes/35 to40% butane feedstock hydrated by passing through water at 40° C. Thereactor effluent was analysed by gas chromatography (GC), feed andproduct olefin/paraffin ratios being compared to determine conversion.Liquid product was analysed on GC equipment having a platinum catalystto hydrogenate olefins to paraffin, carbon number and skeleton beingdetermined. In Comparative Samples C1 and C3 a pure (i.e., sulphur-free)butene feed was used, in Comparative Sample C2 and Example 1 a refineryfeedstock containing 20 ppm sulphur (16 ppm dimethylsulphide, 1.5 ppmdiethyl sulphide, remainder methylethylsulphide and mercaptans) wasused.

The results are shown in the table below. Sample C1 C2 C3 1 Sulphur, ppm0 20 0 20 Temperature, ° C. 225 217 280 281 Days On Steam 7 7 13.6 13.6Total Conversion, % 50.76 33.27 93.04 91.45 Product Mix, % C₄ 2.5 2.582.7 1.62 C₅ 0.77 0.92 0.96 0.92 C₆ 0.15 0.14 0.41 0.37 C₇ 0.26 0.2 1.150.97 C₈ 66.11 71.66 50.77 52.48 C₉ 1.86 2.03 2.8 2.5 C₁₀ 0.63 0.66 1.91.81 C₁₁ C₁₂ 17.21 13.69 25.8 25.29 C₁₃ 1 0.88 1.74 1.6 C₁₄ C₁₅ C₁₆ 9.517.24 11.78 12.44 Sum 97.5 97.42 97.31 98.38 C₇-C₉, % 70 76 56 57C₁₀-C₁₃, % 19 16 30 29 C₁₃+, % 10 07 12 13 C₈/(C₇ + C₈ + C₉) 96.9 9792.8 93.8

Comparative Samples 1 and 2 show that catalyst activity is significantlyreduced by the presence of sulphur at lower operating temperatures(about 220° C.) whereas as shown by Comparative Sample 3 and Example 1the negative effects of sulphur are avoided at 280° C.

The carbon skeletons of the products, after hydrogenation, are shown inthe table below. Example Run C1 C2 C3 1 2,2,4-tri-Me-pentane 0.72 1.10.39 41 2,2-di-Me-hexane 1.17 1.16 1.8 1.8 2,5-di-Me-hexane 2.83 1.59.29 8.99 2,4-di-Me-hexane 11.74 11.88 16.89 16.84 3,3-di-Me-hexane 1.862.74 0.97 0.95 2,3,4-tri-Me-pentane 3.66 5.28 1.61 1.762,3,3-tri-Me-pentane 0.95 1.5 3 0.32 2,3-di-Me-hexane 6.29 6.44 8.618.75 2-Me-3-Et-pentane 2.77 3.62 2.02 2.08 2-Me-heptane 13.17 9.34 14.2214.15 4-Me-heptane 7.48 5.27 7.85 7.8 3,4-di-Me-hexane 18.57 28.75 6.176.47 3-Me-heptane 23.63 17.11 24.73 24.55 n-Octane 5.15 4.32 5.17 5.11C₈ Linear 5.15 4.32 5.17 5.11 C₈ Mono-branched 44.27 31.72 46.8 46.5 C₈Di-branched 45.24 56.08 45.74 45.89 C₈ Tri-branched 5.34 7.88 2.29 2.49C₈ Branchiness 1.51 1.68 1.45 1.46

Example 2

This example illustrates the influence of sulphur on the activity of aZSM-57 catalyst in propene oligomerization and the effect of an elevatedtemperature on that influence.

A 50% ZSM-57/50% alumina catalyst was used to oligomerize a sulphur-freefeedstock of 50% propene/50% butanes at 135° C., at a WHSV of 2.02. Theproduct stream contained about 73% nonenes, 9% dodecenes and 7% hexenesat a total conversion rate of 88%, average degree of branching of thenonenes 1.99.

2 ppm of dimethyldisulphide were added to the feedstock and the runcontinued under otherwise the same conditions. Over the course of 24hours, the catalyst was nearly completely deactivated, shown by a fallin the conversion rate to 5%.

The temperature was then raised to 175° C., when the catalyst recoveredand the conversion rate rose to 95%. The product stream contained about64% nonenes, 11% dodecenes and 5% hexenes, average degree of branchingof the nonenes 1.95.

The example shows that an elevated temperature avoids the deleteriouseffects of sulphur on the activity of the crystalline molecular sievecatalyst, and is effective to re-activate a de-activated catalyst.

Example 3

To the pure feedstock of Example 2 were added 7 ppm ethyl sulphide andoligomerization was carried out at 168° C. over the catalyst used inthat example. The product stream contained about 66% nonenes, 11%dodecenes and 9% hexenes, branchiness of the nonenes 2.0. The conversionrate was 93%.

It was found, using sulphur-free feed, that oligomerizing propene overZSM-22 at 255° C. yielded a nonene product of branchiness 1.57, with 40%of mono-branched isomers. Similarly, using ZSM-22 at 277° C., asulphur-free butene feed yielded an octene product of branchiness 1.15,with 66% mono-branched isomers. A sulphur-containing feedstock wouldyield similar results.

1-35. (canceled)
 36. In a process for the oligomerization of olefinscomprising contacting a feed containing olefin monomers with at leastone oligomerization catalyst having the TON and/or MFS structure underoligomerization conditions, including a reaction temperature, to producea product selected from the group consisting of dimers, trimers, andmixtures thereof, of said olefin monomers, the improvement comprisingsaid feed being further characterized by having from 1 to 100 ppm byvolume sulfur-containing compounds and increasing the reactiontemperature with time the catalyst is on stream.
 37. The process ofclaim 36, wherein said feedstock comprises monomers selected from thegroup consisting of propene, butenes, and mixtures thereof, and saidcatalyst is H-ZSM-57.
 38. The process of claim 36, wherein saidfeedstock comprises monomers selected from the group consisting ofpropene, butenes, and mixtures thereof, and said catalyst is H-ZSM-22.39. The process of claim 36, wherein said feedstock comprises monomersselected from the group consisting of propene, butenes, and mixturesthereof, and said catalyst is H-ZSM-22 and H-ZSM-57.
 40. In a processfor the oligomerization of olefins comprising contacting a feedcontaining olefin monomers with at least one oligomerization catalysthaving the TON and/or MFS structure under oligomerization conditions,including a reaction temperature, to produce a product selected from thegroup consisting of dimers, trimers, and mixtures thereof, of saidolefin monomers, the improvement comprising mitigating the adverseeffects of the presence of sulfur compounds in said feed on at least oneof the activity and life of said oligomerization catalyst by carryingout said oligomerization of olefins at a reaction temperature higherthan that which would otherwise have been chosen for the reactionconcerned in the absence of said sulfur compounds.
 41. The process ofclaim 40, wherein said carrying out is at a reaction temperature of fromabout 220° C. to about 300° C.